High-Resolution Spectroscopy of the Transiting Planet Host Star TrES-1

We report on a spectroscopic determination of the stellar parameters andchemical abundances for the parent star of the transiting planet TrES-1. Basedon a detailed analysis of iron lines in our Keck and HET spectra we derive$T_\mathrm{eff} = 5250\pm 75$ K, $\log g = 4.6\pm 0.2$, and [Fe/H] $= 0.00\pm0.09$. By measuring the \ion{Ca}{2} activity indicator and by putting usefulupper limits on the Li abundance we constrain the age of TrES-1 to be $2.5\pm1.5$ Gyr. By comparing theoretical stellar evolution models with theobservational parameters we obtain $M_\star = 0.89\pm 0.05$ $M_\odot$, and$R_\star = 0.83\pm 0.05$ $R_\odot$. Our improved estimates of the stellarparameters are utilized in a new analysis of the transit photometry of TrES-1to derive a mass $M_p = 0.76\pm 0.05$ $M_\mathrm{J}$, a radius $R_p =1.04^{+0.08}_{-0.05}$ $R_\mathrm{J}$, and an inclination $i =89^\circ.5^{+0.5}_{-1.3}$. The improved planetary mass and radius estimatesprovide the grounds for new crucial tests of theoretical models of evolutionand evaporation of irradiated extrasolar giant planets.Comment: 14 pages, 3 figures, Astrophysical Journal Letters, accepte